fix(core): Fix corner cases in initialized range tracking

[andyleiserson]

Adds a proptest for the uninitialized range tracker, and fixes a few corner cases.

This does add a new dev-dependency on proptest; I think these are good tests and this probably isn't the only place where we could benefit, but every dependency costs something.

Testing
The proptest; also includes directed tests for the fixes.

Squash or Rebase? Squash

Checklist

• I self-reviewed and fully understand this PR.
• WebGPU implementations built with wgpu may be affected behaviorally.
• Validation and feature gates are in place to confine behavioral changes.
• Tests demonstrate the validation and altered logic works.
• CHANGELOG.md entries for the user-facing effects of this change are present.
• The PR is minimal, and doesn't make sense to land as multiple PRs.
• Commits are logically scoped and individually reviewable.
• The PR description has enough context to understand the motivation and solution implemented.

[andyleiserson]

It looks like our use of rand 0.8 is via noise, for the water example.